Data storage media, such as magnetically encodable discs in disc drives or optically encodable discs in readable/writable compact disc drives or digital video disc drives, typically contain interspersed regions of servo data and user data. The servo data is typically encoded upon the disc at the time of manufacture, and is used for the purpose of letting the storage mechanism (disc drive, readable/writable CD ROM, etc.) determine the location over which its transducer (read/write head) is located. The regions of user data contain data stored by the user.
Generally, data is read from a storage medium by a read/write channel. The read/write channel receives analog waveforms transduced from the storage medium (a pre-amplifier may be interposed between the transducer and the read/write channel), and converts the analog waveforms into digital form. The digital form may be subsequently processed by a digital stage within the read/write channel. Thereafter, the digital information is communicated to a controller.
Usually, servo data and user data are encoded on the disc in differing formats. Thus, the process of converting an analog servo waveform (a servo burst) into digital data for the controller is different from the process of converting an analog waveform containing user data into digital data for the controller. Because the transformation process varies between servo and user data, a read/write channel functions in only a single mode at any one time. In other words, the read/write channel initially functions in a mode for conversion of servo data. When all of the servo data has been recovered and communicated to the controller, the read/write channel then transitions to a mode in which it recovers user data.
The above-described process exhibits certain shortcomings. For example, there generally exists a latency period from the time an analog waveform is received by the read/write channel to the time the converted information encoded in the waveform is communicated to the controller. Consequently, after all of the servo data has been received by the read/write channel, the read/write channel does not begin reading or writing user data until the latency period has lapsed (i.e., until all of the servo data has been communicated to the controller). Upon lapsing of the latency period, the read/write channel reads/writes user data.
During the latency period, the data storage medium continues to spin. Since no data is read from the medium during the latency period, the latency period corresponds to a literal blank space on the surface of the medium-space in which no data is recorded, because it will not be read. Thus, storage media usually contain a region of servo data, followed by a region of empty space (referred to as a “pad” region) corresponding to the latency period, followed by user data. The aforementioned pad region contains no data whatsoever, and is therefore wasted space.
As is evident from the foregoing, there is a need for a scheme by which the latency period can be diminished. By diminishing the latency period, its corresponding pad region is reduced, and the amount of medium surface devoted to storing user data is increased. Thus, the storage capacity of the medium increases. A successful scheme will be relatively inexpensive and easy to implement.